There's certainly welding...
JJ's thing he calls Trek looks more primative than Enterprise, even Archer's warp core looked more advanced.
Stopping the construction of ships in space with robots and little work pods and replacing them with a bunch of sweaty guys with arch welders seems going backwords. And the TNG warpcore seemed small, sleeker and much more compact than JJ's brewery, which he did NOTHING to hide that.....looked bad in the original V and looks bad today, also. Surprised JJ did nit opt for the welders to use acetylene torches.
As for no nuts and bolts, it's newer techniques, newer technology. In "Wounded Sky", it was mentioned the hulls were 'woven', almost like how spiders or silk worms, or even bees making their webs, silk or hives. I really like the idea of that. Also, Doctor Who, Castrovalva to be exact, showed Nissa using a device that does, as she says it, molecular adjustment. Also, from my own UFO studies (gets ready for ridicule and infantile natured captioned pictures), according to eye witnesses, including, recently, ex-military personal, the hulls of many of the ships appeared to be a single piece, no joins, seems or anything like that, as if the ship was poured or even grown as opposed to being built, and the materials feeling as if they were almost nearly there, being that light. Even changing colors in reaction of thought, since the ships, seemingly, were controlled by thought rather than an actual control panel.
Whatever way they do it on Trek, it's gotta be a lot more advanced than a bunch of hot, smelly guys in overalls with arc welders.